An X-ray flat panel detector is a part of a large-area planar X-ray imaging system. X-ray radiation passing through an irradiated object is converted into an electronic signal by the X-ray flat panel detector, and then a digitized gray scale image directly relating to the internal structure of an irradiated object is formed. By using the X-ray flat panel detector, a non-destructive internal imaging of the object can be realized, which is one preferable way to realize a non-destructive inspection. The X-ray flat panel detectors have wide applications in medical and technology, and great progress has been made in the fields of medical imaging examination, industrial nondestructive imaging detection and inspection, and the like.
As illustrated in FIG. 1, the X-ray flat panel detector includes an X-ray fluorescent layer 1, a flat panel sensor 2, image acquisition chips 3 and a peripheral logic control and image processing system 4. Specifically, an image acquisition chip 3 includes a switch control chip 31 and a signal read-out chip 32. The flat panel sensor 2 used in the X-ray flat panel detector illustrated in FIG. 1 is an indirect flat panel sensor which only absorbs visible light and light with wavelength close to that of the visible light. Thus, the X-ray fluorescent layer 1 needs to convert the X-ray into the visible light such as green light or blue light. In another X-ray flat panel detector, the flat panel sensor 2 used is a direct flat panel sensor, which can absorb X-rays directly and in this case, the X-ray fluorescent layer 1 may not be needed.
The flat panel sensor 2 includes a large pixel array and a transparent substrate. The pixel array is one of the core components in the X-ray flat panel detector and is disposed on the transparent substrate (e.g., a glass substrate, a quartz substrate). The pixel array includes a plurality of control lines 22 extending along the X axis direction and a plurality of read lines 23 extending along the Y axis direction, the X axis and the Y axis are substantially orthogonal to each other. The region surrounded by two adjacent control lines 22 and two adjacent read lines 23 forms a pixel region, in which a pixel unit is disposed. Each pixel unit 21 includes a photosensor 211 (e.g., a photodiode) and at least one switching element 212 (e.g., a thin film transistor, TFT). The state of switching element 212 is controlled by a control signal on the control line 22. When switching element 212 is turned on, the signal in the pixel unit 21 which in the same pixel region as switching element 212 can be read by the read line 23. When the switching element 212 is turned off, the signal in the pixel unit 21, which is in the same pixel region as the switching element 212, cannot be read by the read line 23. Specifically, in a case where the switching element 212 is a TFT, for example, the TFT is disposed at the intersection between one control line 22 and one read line 23, and the pixel unit 21, which is in the same pixel region as the TFT, is coupled to the control line 22 and the read line 23 via the TFT. The coupling means that a gate electrode of the TFT is electrically connected to the control line 22, a source electrode/drain electrode of the TFT is electrically connected to the read line 23, and a drain electrode/source electrode of the TFT is electrically connected to the pixel unit 21. The size and number of the pixel units 21 may affect the resolution and the area of the image.
X-rays passing through the object under detection can be converted into visible light by the X-ray fluorescent layer 1, and the visible light is projected onto (or the X-rays passing through the irradiated object are directly projected onto) the photosensors 211 of the flat panel sensor 2. The photosensors 211 generate electric charges in a corresponding proportion and temporarily store them in the pixel units 21 of the flat panel sensor 2. When a control signal is applied to one control line 22 and the switching element TFT 212 of which the gate electrode is electrically connected to the control line 22 is turned on, the electric charge signal temporarily stored in the photosensor 211 can be read out by the read line 23 which is electrically connected to the source/drain electrode of the switching element TFT 212. An analog-to-digital conversion or another corresponding processing is then performed on the electric charge signal.
The peripheral logic control and image processing system 4 controls the image acquisition chips 3 to function properly, so as to turn the switching element TFTs 212 in each row of the pixel units 21 on or off and to read and process the charge signals in the photosensors 211 in respective pixel units 21. The switch control chips 31 sequentially turns on the switching element TFTs 212 line by line via the control lines 22. While the switching element TFTs 212 are turned on, the signal read-out chips 32 read out the charge signals temporarily stored in the pixel units 21 via the read lines 23, perform the analog-to-digital conversion, and transmit the processed digital signals to the peripheral logic control and image processing system 4. In this way, the image acquisition is performed line by line until all of the charge signals in the pixel units 21 of the whole flat panel sensor 2 are read out, so that the complete image is read and processed.
As illustrated in FIG. 2, in the prior art, the image acquisition chip 3 is mounted on a flexible printed circuit board (FPC) 5 by a chip on film (COF) bonding process. The image acquisition chip 3 and the FPC 5 are packaged together and form a COF module 6. Then the COF module 6 is bonded onto a conductive contact 24 of the flat panel sensor 2 by a film on glass (FOG) bonding process, so that the flat panel sensor 2 and the image acquisition chip 3 are electrically connected to each other. In the FOG bonding process, the conductive contact 24 of the flat panel sensor 2 is coated with an anisotropic conductive film (ACF) 7, then the FPC 5 of the COF module 6 is connected to the conductive contact 24 of the flat panel sensor 2 by a hot pressing process. The ACF 7 conducts electricity in one direction only (the vertical direction), but does not conduct electricity in other directions (e.g., the horizontal direction). Therefore, the COF module 6 is in conductive connection with the conductive contact 24, but is electrically isolated from adjacent conductive contact(s). Of course, in the conventional art, the COF module 6 may also be metal-welded to the conductive contact 24 of the flat panel sensor 2, so that the flat panel sensor 2 and the image acquisition chip 3 are electrically and physically connected to each other.
In normal mode of operation or test mode of operation, if the flat panel sensor 2 has a problem and does not meet performance requirements, and the COF module 6 has to be removed from the flat panel sensor 2. The FPC 5 in the COF module 6 may be damaged in the removal process due to the sticking and hot pressing process or the metal-welding process of the ACF 7 and the flexible feature of the FPC 5, resulting in a non-operation of the entire COF module 6. However, the image acquisition chip 3 in the COF module, although not damaged, cannot be recovered and reused (i.e., recycled) due to damage of the FPC 5, leading to waste of otherwise good image acquisition chips.
Worse yet, not only in the case of the X-ray flat panel detector, the image acquisition chip 3 cannot be recycled, leading to resources waste, as described above, but also in the case of other devices (e.g., touch screens, flat panel displays) where the chip unit and the flexible connecting device are packaged in a COF module which is then connected to the substrate unit of the device by ACF bonding or metal-welding, the image acquisition chips cannot be recovered and reused due to damage of the flexible connecting device in the COF module during the removal process, resulting in enormous waste of otherwise reusable chips.